1. Field of the Invention
This invention relates to blotting test apparatus. More particularly this invention relates to a positive pressure blotting apparatus for biological molecules.
2. Description of the Prior Art
Blotting membrane based tests for biological samples have become common. The The tests are described in an article by Leary, Proc. Natl. Acd. Sci. USA, Vol 80, pp. 4045-4049, (1983). A standard apparatus for blotting or dot blotting onto membranes can be purchased can be purchased from many different suppliers. Each supplier appears to have a special design to accelerate filtration, avoid migration of test points, referred to as "cross-talk", and otherwise protect samples from contamination.
As the size of the biological molecule increases, greater difficulty is experienced in filtering the sample to bind the molecule to the filter material. In all of these devices, attempts are made to improve the filtration rate by applying negative pressure to the filter medium by creating a vacuum in the chamber under the filter medium.
Some in the prior art have suggested that applying positive or negative pressure are equivalent however, in all specific examples, negative pressure is used. Olsen, et al., in U.S. Pat. No. 4,853,335 describes using positive or negative filtration in a colloidal gold particle concentration immunoassay. Matkovich, et al., in U.S. Pat. No. 4,797,259, describes an improvement in "well-type" diagnostic plate devices in which the use of positive and negative pressure are considered to be equivalent. Matkovich suggests that in both cases it is necessary to wet the filter material. Normally hydrophobic membranes, such as polyvinylidene fluoride, must be made hydrophilic in order to operate in the Matkovich invention. Matkovich renders the polyvinylidene fluoride hydrophilic by washing with reagents such as methanol. Matkovich suggests that applying positive pressure up-stream of the membrane is equivalent to applying negative pressure down-stream of the membrane, but Matkovich illustrates only the use of negative pressure. Nothing in Matkovich provides evidence which supports the allegation of equivalence.
Methanol and other reagents used to render a membrane hydrophilic can denature or otherwise change the biological molecules which the blotting technique seeks to recover or analyses. It is preferred to have an apparatus and technique which avoids using damaging or denaturing reagents.